Signal conversion system



Feb. 26, 1952 P. SMITH SIGNAL CONVERSION SYSTEM Filed NOV. 28, 1947 4Sheets-Sheet l m '5mm l EY ffy- HTTRA/EY Feb. 26, 1952 J. P. SMITHSIGNAL. CONVERSION SYSTEM 4 Sheets-Shea?I 2 Filed NOV. 28, 1947 Z5cazzfcm? 55,1255

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SIGNAL CONVERSION SYSTEM Filed NOV. 28, 1947 4 Sheets-Shea?l 5 65.77 bg/nf jm m WINT-r /W 200x +/5. /IJK/MK I 65.77 l

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SIGNAL CONVERSION SYSTEM Filed NOV. 28, 1947 -4 Sheets-Sheet 4 1|, S lwww ww N l# .M y @we dill Patented Feb. 26, 1952 SIGNAL CONVERSIONSYSTEM John Paul Smith, Cranbury, N. J., assignor to Radio Corporationof America, a corporation of Delaware Application November 28, 1947,Serial No. 788,511

4 Claims. (Cl. 178-5.2)

'Ihis invention relates to the conversion of one signal type to anothersignal type, and particu? larly the conversion of simultaneous typecolor television signals into sequential type color television signals.

Many important types of electric signaling areconcerned not only withthe transmission of intelligence, but are concerned with the sequenceand order of its transmission. For such types of electrical signaling,sync impulses or other synchronizing information usually accompany thetransmission of the intelligence.

Along with the development of these various types of signaling has comethe requirement for conversion from one particular type to anotherparticular type involving a different order of transmission or adiierent standard.

An important example is suggested by the transmission of colortelevision signals.

Y It is quite well known that the transmission of images by electricitycan be accomplished by analyzing the image into its image elements andforming a signal train of impulses by a predetermined orderly sequenceof scanning. 'I'he image may then be reproduced at a remote location bythe same sequence of scanning.

' It is also Well known to the optical art that the reproduction ofimages in color may be accomplished by additive methods, that is,breaking down the light from an object into a predetermined number ofselected primary or component colors which are three in number for atricolor'` system or, for a compromised degree of delity of colorrepresentation, even a bicolor system may be employed.

Color images may therefore be transmitted by' electricity by analyzingthe light from the object into not only its image elements, butby alsoanalyzing the light from elemental areas of the Aobject into selectedprimary or component colors and forming a signal train of impulsesrepresenta-- tive of each of the selected component colors. A-

1 color component image, the target electrodeis scanned in proper phaserelationship with respect to the color image exposures to enable thetrans-- mission of signals representing the corresponding colorseparation image.

` In the conventional sequential multicolor television receiver, akinescope or other image reproducing tube is employed to recreate ablack and white image likeness which is viewed or projected through a,color lter of the selected component color corresponding to the desiredcomponent color instantaneously being represented. The process is thenrepeated for the next selected color component, and so on.

A typical vsequential color television system is shown and described inan article entitled "An Experimental Color Television System, beginningon page 141 of the RCA Review for June 1946.

A simultaneous al1-electronic color television system has been proposedinvolving a cathode ray scanning tube which forms a scanning raster tobe projected on a color iilin from which selected color component lightsensitive devices transform the resultant light into several separatesignal trai's, each representative of a selected component color. Asystem of this nature is sometimes referred to as the vflying spotsystem, and is f shownV and described in an article entitledSimultaneous All-Electronic Color Television, beginning on page 459 ofRCA Review for December 1946. v l

Other systems of simultaneous electronic color television have beenproposed involving the simultaneous employment of several image pickupdevices and several corresponding image producing' devices which areadapted to combine the several component color images to form acomposite image in substantially its natural color.

According to one form of this invention, signals which are picked up bythe simultaneous method (as, for example, the method referred to) may beconverted into signals which are Suitable for reproduction in'devicesadapted for the sequential type of color television image signals.

According to this invention, predetermined portions of a signal trainare stored and retransmitted in accordance with a predeterminedarrangement.

In my copending United States application, Serial No. 782,803, ledOctober 29, 1947, circuit arrangements are shown for convertingsequential type television signals and the like into simultaneous typetelevision signals and the like.

A primary object of this invention is to provide for the conversion ofintelligence signals of one type into intelligence signals of anothertype.

Another object of this invention is to accurate- 1y convert televisionsignals of the simultaneous type into television signals of thesequential type.

Other and incidental objects of the invention will be apparent to thoseskilled in the art from a reading of the following specication and aninspection of the accompanying drawing in which Figure l illustrates byblock diagram'onelorm of this invention adapted to convert simultaneoustelevision signals into sequential television signals;

Figure 2 shows a detailed illustration of afsterage tube suitable foremployment in thepractice of this invention; and

Figures 3, 4, 5, 6 and? show by circuitdiagram details of the componentsshown in block in Figures l and 2.

Turning now in more detail tothe block diagram in Figure l, asimultaneous type color signal of three independent selected componentcolor signal trains is applied to storage'tubes 4A, B and C during oneinterval, and storage tubes D, E and F during the succeeding timeinterval. Atvthe time that the simultaneous video signal trains areVapplied to storage tubes A, Band C, storage tubes D, E and F are keyedto operate sequentially to produce a sequential Video signal. Likewise,while the simultaneous type video signal trains are applied to storagetubes D, E and' F, storage tubes A,B and C are keyed sequentially toform the sequential video signal output train.

The selection required to apply the simultaneous video signal input tostorage tubes A, B- and C is accomplished by operating switching devicesK23, KZll and K to pass the simultaneous-video signal through ampliiiers5, I and B'tolstorage tubes A, B and C. Switching devces'KB, 'K2` andK25, like the other of the switching devices of vFigure 1 indicated by ablock and a letter iK followed by a number, may be of the type"illustrated in detail in the circuit diagram'ofFigure 6. Other switchingdevices may be substituted therefor, provided, of courseytheyoperate-sunlciently rapidly and accurately.

The switching devices K23, K24 and K25-'are adapted to pass signals onlywhen the control pulse received from polarity reverser II in the centerof the drawing takes, for example, a. positive direction. Polarityreverser I I4 may,-for'pur poses of illustration,'take the form ofa-multiv-ibrator circuit arrangement, such as'that-shown in detail inFigure 3. The polarity reverser II located in the center of thediagram-is driven by a synchronizing pulse to form a square wave. Thepotential'furnished in the lea'd to`=the left ofthe polarity reverser is180 out of phase-With the potential furnished in the lead to vthe-rightof the polarity reverser II.- Y

During the time interval that switches `X23, KM and K25 are passing thesignal, the PQIW reverser II furnishes an opposite control potential toswitches K26, K2? and K28 to prevent switches K26, K21 and K28 frompassing the simultaneous signal.

During the time interval that storage tubes A, B and C are receiving thecharge by reason of switches K23, Kill and K25 being operative, switchK22, located at the bottom of the drawing, is energized to pass signals.It will be noticed that switch K22 receives the same control voltagefrom polarity reverser Il as do switches K23, KM andK25.

It is necessary, however, that storage tubes D.

-E andF be keyed sequentially during the discharge interval in order toproduce in ampliner 3 a sequential type video signal. This isaccomplished by making storage tubes D, E and F operable sequentially bycontrolling their operation withthe application of a keying voltage totheir control electrodes. This is accomplished by applying a readingpotential to their control electrodes through switches KI 5, KI 8 andK25, which receive their excitation from both the polarity reverser IIandring frequency divider I3. Polarity reverser II prepares all switchesKIS, KIS,

and Kili for operation, while ring frequency divider I3causes them tooperate sequentially.

Ring frequency divider 3 is shown and described in detail under Figure 5below. .It produces a series of control pulses arranged sequentially.y

It will thus be seen v that during theinterval in which storage tubes A,B and C are receiving their charge, storage tubes D, E and F are givingup their charge sequentially.

Switches,K9,-KII and KIS operate to establish on the control-electrodesof tubes A,- B andl C dur.- ing their storage time an appropriatepotential for the laying down or writing phase of theoperation. SwitchesK9, K! I and KIS are each colinected to the polarity reverser II to beactuated` at the same time as switches X23, X24 and K254 arev madeoperative.

During the succeeding time interval, switches K26, Kill and K28 are madeoperable to storage signals on storage tubes D, E and F, while switchesK23, K24 and K25 are opened. At the time stor-1 age tubes D, E and F arereceiving their charge, storage tubes A, B and C are operatedsequentially by switches .KI-, Kil. and KM to provide a sequential videosignal through switch K2! and amplifier I.

The timing of the switching from one group of storage tubes to the otheris determined by the synchronizing signal recurring rate.v Accordingtoone form of the invention, the synchronize ingsignal isv the same asthat employed in the over-all television system, which normally is basedon the commercial power supply frequency oi Si? cycles per. second. Thecycle per second synchronizing signal necessary for the ring frequencydivider I3 may be obtained from the 60 cycle synchronizing signalthrough a frequency multiplier such as, forexample, the circuitarrangements shown in Figure 4.

In the ormof the invention shown in Figure l, the timing is arranged sothat, during the interval occupied by the sequential vdeo signalrepresentative of, for example, one selective component color, storagetube A is actuated. Likewise, during the occurrence of asequentialvvideo signal representative of another component color,

tial colonstorage tube C is operative. This perassmo mits thedesignation of one of storage tubes A, B and C to be operative at a timeduring the discharge action. The same is true with storage tubes'D, Eand F.

In converting simultaneous video signals to sequential video signals, itis also necessary that a different rate of scanning be employed in thelaying down of the signal and also the picking up of the signal. This isaccomplished by the employment of two sets of scanning standards for thescanning elements of the storage tubes.

At the top of the drawing, there is illustrated input circuits forhorizontal and vertical sawtooth wave deflection voltage both at thesimultaneous rate and sequential rate. Through switches KI to K8inclusive, appropriate scanning energy is supplied to horizontalamplifier I5, vertical amplifier I 1, horizontal amplifier I9, andvertical amplifier 2 I.

The generation and application of deflection currents to the cathode raybeam deflection tubes is well known in the art, and may take any of anumber of' well known forms. For purpose of illustration, however, thereis shown in detail in Figure '1 of the drawing a suitable deflectioncircuit arrangement.

It will be noticed that horizontal amplifier I5 and vertical amplifierI1 are connected to the sources of simultaneous deflection voltage atthe same time switches K23, K24 and K25 permit the transmission ofsimultaneous type video signals to the storage tubes A, B and C,`likewise horizontal amplifier I5 and vertical amplifier 2| are connectedto the source of simultaneous deection voltage at the time switches KZ6,K21 and K28 permit the transmission of simultaneous video signals tostorage tubes D, E and v During the time, however, that the signal ispicked up from storage tubes A, B and C, the sequential deection signalvoltages are applied to horizontal amplifier I5 and vertical amplifierI1.

Turning now in more detail to Figure 2, there is illustrated onesuitable type of storage tube 23 which is commercially known as the STEtype.

There are other types of storage tubes which are suitable. One othertype, known commercially as the BDT-5, is shown and described in detailin a copending application of Richard L. Snyder, Jr., entitled ElectronTubes, Serial No. 606,812, and led July 24, 1945, now Patent No.2,548,405, granted April 10, 1951.

A simultaneous type television camera 25 transmits its simultaneousvideo signal through video amplifier 21 to a series of switches23,illustrated in block for convenience in Fig. 2. The detailed circuitarrangement connecting switches 2S of Figure 2 to their associatedstorage tubes may be similar to that shown in Figure 1, however, for thepurpose of simplification of explanation of Figure 2, a single storagetube 23 is employed.

Likewise, the connections to the sequential television transmitter 3|are obtained through a group of switches 33 in a manner described underFigure 1 above.

Although the detailed operation of storage tube 23 is known to the art,it may be well to brieiiy review its operation in order to insurecomplete understanding of the operation of applicants in Vention. Thestorage tube type STE records electrical signals from the switchingdevice 29 in the form of charges distributed over a dielectric surface35 and reproduces the record by remov-l ing the charges with an electronbeam 31 generated in an electron gun 39 directed at the dielectricsurface 35. Charges of either polarity may be stored; negative chargesare caused by the deposition of primary beam electrons and positivecharges are caused by the extraction of secondary electrons 38 resultingfrom the impact of the electrons of the beam 31. Reproduction of thestored signals is accomplished by the same mechanism as that used inrecording, but is carried out with no signal input. The beam 31 from theelectron gun operates at constant current, except when it is blankedduring blanking or standby period. The number of secondary electrons 38generated by the beam on striking the dielectric surface 435 iiuctuatesin a manner dependent upon the deposited charge. This secondary current,which is of low intensity, represents the output signals of the deviceand is available from collector electrode 40.

The dielectric surface 35, which forms the target electrode for theelectron beam 31, is one side of a thin insulated layer, which ismounted with its other side in intimate contact witha conducting plate45. Over the exposed surface is stretched a ne metal screen 41, whichhas a high void-to-land ratio.

In operation, the electron beam 31 strikes the dielectric surface 35with suicient velocity to produce a secondary emission ratio greaterthan unity. To obtain this condition, the cathode of the electron gun 39is maintained at ground potential, and a potential of about 1100 voltsis applied to the target screen 41. With this arrangement, wherever thebeam 31 strikes the dielectric 35, the potential of an elemental area ofthe surface under bombardment becomes the same or nearly the same asthat of the screen 41, that is, equilibrium conditions exist only atthis potential.

If an elemental area of the dielectric surface 35 is negative relativeto the screen 41, a positive field is presented to the surface 35, andtherefore all of the secondary electrons released by the impact of thebeam electrons of beam 31 are drawn away. Since the number of secondaryelectrons is greater than the number of primary electrons, there is anet loss of negative charge, and the surface 35 changes in a positivedirection. If, however, an elemental area of surface is positive withrespect to the screen 41 at the time of bombardment, a negative field ispresented to the surface and secondary emission is suppressed. Since nosecondary electrons leave the elemental area of the dielectric surface35 `under such a condition, there is a net gain of negative charge andthe potential of 35 changes in a negative direction.

At the potential of the screen 41 or a little positive thereto, the twoeffects balance. Just enough the surface of the secondaries leave thesurface to neutralize Y the arriving primaries. This condition of unitysecondary emission equilibrium probably exists at a potential a fewvolts positive with respect to the screen 41 because the linitialvelocity of most of the secondary electrons is suicient to lift themover a 2 to 4 volt barrier. The exact potential is not very definitebecause it is affected by space charge conditions and the geometry ofthe screen 41 and nearby electrodes.

' The value of the equilibrium potential has substantially no influenceon the operation of the tube as long as it remains substantiallyconstant.

In the normal operation of storage tube 23, the screen 41 is maintainedat a D.C. potential of 1100 volts, and thevconductor 45 on the back ofthe dielectric is connected to the source of signal to be recorded,which in this form of the invention is obtainedfrom switches 29. Therecording surface 35 is therefore capacity coupled to the signal plate,and also has capacity to the screen 41. When the signal voltage isimpressed upon the signal plate 45, it also appears somewhat diminishedin amplitude on the recording surface 35.

If, then, the beam 31 is .deflected across the surface 35 while a signalis impressed on the signal plate 45, it will cause each element itstrikes on surface 35 to come to the potential of screen 41 regardlessof the potential the surface would otherwise have due to the influenceof the signal plate. This action then establishes a charge between thesignal plate 45 and the surface element on the surface 35, which willcause the element to have a potential different from that of the screen41 when the beam moves elsewhere and the signal plate 45 returns to zeropotential. If the beam scans a long path over the target 35 while aiuctuating voltage is impressed on the signal plate d5, a band ofcharges as wide as the beam 31 will remain on the path when the beam iscut off or traverses elsewhere on the target 35.

If the signal plate 45 returns to zero potential, the potential alongthe scanning path on target 35 will vary in proportion to the signalvoltage impressed during the beam transit. It will, orcourse, be smallerthan the impressed voltage and its polarity will be reversed. During thenext scansion by the electronbeam 31 which may, for example. be thepickup scansion, a stream of secondary electrons is released from target35. Some of the secondaries are released from the solid parts of thescreen 41 which intercepts some of the beam current. The rest come fromthe surface of the dielectric 35. Although the secondary emission ratioof .the screen 41 is constant, the secondary emission from thedielectric surface fluctuates according to the previously assumed chargeof the scanned elemental area. If a negative charge is to be supplied,secondary emission ceases until the demand has been satisfied. If apositive charge is needed, the secondary emission is at maximum untilthe full charge is achieved.

The iluctuations of the secondary electrons during the picking upscanning period, therefore, constitute a signal equivalent to the signaldeposited in the previous scanning operation. It

is therefore possible .to delay a portion of the signal train in thestorage tube 23 in order that it may be transmitted through sequentialtelevision transmitter 3l in accordance with another desired standard.

Figure 3 illustrates by circuit diagram the combination of amultivibrator involving tubes 49 and-l which produces, as is well knownto the art, a square wave to excite the control electrode of tube 53.Tube 53 has two output circuits, one connected to its anode .and anotherconnected to its cathode. The square wave output of each output circuitof tube 453 is therefore out of phase with each other by 180. The outputcircuit of tube 53 connected to its anode may, for example, be theleft-hand output circuit of the polarity reverser il of Figure 1, whilethe lower output circuit connected to the cathode of tube 53 may be theright-hand output of polarity reverser Il of Figure l.

Figure 4 shows in circuit diagram vdetail a suitable requency multiplierwhich may be employed in the practice of this invention to convert 60cycle synchronizing pulses into 180 cycle synchronizing pulses. By theuse of this circuit in i and 89.

connection with the block diagram of Figurel, it is possible to have aexible system adaptable for use with 60 cycle synchronizing pulses.

Tubes 55 and 51 are employed as a multivibrator in the well known mannerto produce a triple frequency pulse of the cycle input synchronizingsignal. The operation of the multivibrator including tubes 55 and 51depends for its output frequency on the circuit constants which areindicated on the drawing. The circuit constants are so chosen that themultivibrator completes three cycles of operation for each triggering orsynchronizing input pulse.

The cycle pulse is then properly shaped and amplified in tubes 59 and6l.

The circuit arrangement shown in Figure 4 is also by way of example.Alternate methods of frequency multiplication are, of course,satisfactory for employment in the practice of this invention.

Figure 5 shows in detail one form of ring frequency divider which may beutilized in the block I3 in the lower left-hand corner -of Figure 1. Aninput signal is applied to the circuit of Figure 5 in the upperleft-hand corner, as indicated.

The operation of ring frequency divider, as illustrated in Figure 5. isalso well known in the art and needs no further description here, exceptto call attention to the fact that the output signal of the ringfrequency divider, as indicated on the right-hand side of Figure 5.provides three recurring sets of pulses, each 1/180 second in durationand spaced 1/@0 second. It will be seen. therefore, that the pulsesobtained from the ring frequency divider I3 of Figure 1 actuate switchesK9 through KZll and make operative the proper storage tubes in propersequence. A circuit arrangement for producing the same result in adierent manner is shown and described, for example, in Somers U. S.patent application, Serial No. 417,295, led October 31, 1941. now PatentNo. 2,505,589, granted April 25, 1950.

Figure 6 shows in circuit diagram one satisfactory type of keyer whichmay be employed in any of the key positions of Figure 1. The videosignal is applied to one control electrode of tube 15, while the keyingsignal obtained from the keyer shown in Figure 3 is applied to anothercontrol electrode. The video signal obtained from the anode of tube 15is therefore passed only during the desired intervals.

Figure 7 shows by circuit diagram a suitable deection signal generatorand amplifier which may be employed in the practice of this invention.The circuit shown in Figure 7 may, for example, be substituted for theblock of Figure l designated as a horizontal deection amplier andassociated switching blocks.

The sequential synchronizing pulse is applied to tube 11 which acts toform a sawtooth wave in resistance condenser combination 19 and 8l.

Tube 83 acts as a switch to feed the sawtooth Waves to the inverter 85,which produces a pushpull sawtooth Wave through amplifier tubes il Thesawtooth waves are then applied to the deflection plates of the storagetubes, as designated.

The synchronizing sawtooth wave formed by tube i1 is also transmitted toswitch K5 at the bottom of the drawing to be applied to other amplifiersand deflection plates, as shown and described in connection with thedescription of Figure 1. y

lThe simultaneous synchronizing pulse is applied to tube 9i, whichlikewise forms a sawtooth Horizontal Vertical Capacitor DeflectionDeflection System System 100K ohms 50K ohms variable 1M ohms. 1M ohmsvariable. 10M ohms. 1M ohms.

1000 ohms.

150 ohms. 100K ohms.

2200 ohms. 10K ohms. 68K ohms. 250K ohms.

250K ohms I Values of capacitors, resistors and voltages, together withtube types, have been given in connection with the drawings in Figures3, 4, 5 and 6 for the purposes of example only. Any suitable values ofcapacity, resistance, inductance and voltages, as well as tube types,may be substituted therefor without departing from the spirit of thisinvention.

Having thus described the invention, what is claimed is:

1. A system for converting color television signals of the simultaneoustype into color television signals of the sequential type comprising asimultaneous type color television signal channel, a sequential typecolor television signal channel, two groups of a plurality of signalstorage tubes, a rst switching means to simultaneously connect each ofone group of said storage tubes to said simultaneous type colortelevision signal channel, means connected to said rst switching meansto periodically actuate said first switching means periodically, asecond switching means to sequentially connect each of the other groupof said storage tubes to said sequential type color television signalchannel, and means connected to said second switching means toperiodically actuate said second switching means periodically.

2. A system for converting color television signals of the simultaneoustype into color television signals of the sequential type comprising asimultaneous type color television signal channel adapted to transmiteach of a plurality of signal trains representative of a selectedcomponent color, a sequential type color television signal channel, aplurality oi storage tubes, switching means to simultaneously connectsaid simultaneous type color television signal channel to one group ofsaid storage tubes in a manner such that signals representative of eachselected component color are applied to one storage tube or said group,means to operate said switching means in synchronism with the scanningrate of said simultaneous system, a second switching means tosequentially connect each of the signal storage tubes of another groupof said storage tubes to said sequential type color television signalchannel and means to operate said second switching means in synchronismwith the scanning rate of said sequential system, and wherein both ofsaid switching means operate to connect different groups of said signalstorage tubes at all times.

3. A method of converting signals of one type to signals of anothertype, comprising the steps of individually storing a rst plurality ofsignal trains simultaneously during a rst time interval of predeterminedduration, reproducing sequentially in concurrence with the storage ofsaid rst plurality of signal trainsall of a second plurality of signaltrains previusly individually stored simultaneously during a precedingtime interval of the same predetermined duration, and subsequentlyreproducing all of said first plurality of signal trains sequentiallyduring a succeeding time interval of the same predetermined durationwhile concurrently individually storing a third plurality of signaltrains simultaneously.

4. A method of converting groups of television image signal trainsoccurring simultaneously during successive time intervals each of thesame predetermined duration into groups of television image signaltrains occurring sequentially during said successive time intervals,comprising the steps of effecting a rst individual storage of saidgroups of simultaneous image signal trains respectively during oddnumbered ones of said time intervals, effecting a second individualstorage of said groups of simultaneous image signal trains respectivelyduring even numbered ones of said time intervals, effecting respectivelyduring said even numbered time intervals a rst sequential reproductionof said first simultaneously stored groups of image signal trains, andeffecting respectively during said odd numbered time intervals a secondsequential reproduction of said second simultaneously stored groups ofimage signal trains.

JOHN PAUL SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,253,292 Goldsmith Aug. 19, 19412,309,506 Herbst Jan. 26, 1943 2,335,180 Goldsmith Nov. 23, 19432,423,769 Goldsmith July 8, 1947

